This invention relates to the manufacture of rechargeable electrochemical cells and, more particularly, to the filling of such cells with liquid electrolyte. A typical electrochemical cell, such as a nickel-cadmium cell, is formed of positive and negative electrode plates having an intermediate separator layer of porous material, the electrode plates and the separator being rolled into a cylindrical electrode coil, or roll, which is inserted in an open-ended cylindrical cell casing. Prior to closing the top of the casing, a liquid electrolyte is added, the liquid soaking into the porous separator material so as to maintain an electrolyte solution between the positive and negative electrode plates. A problem arises in the manufacture of such cells in that the porous material of the spacer absorbs the electrolyte at a rate which is relatively slow compared to the speed of other steps in the automated manufacture of such cells. Typically, in the fabrication of the cells, the cans containing the cell roll are supported on a rotary index table which rotates to transport the cells from station to station to accomplish such steps as the filling of the cells and the sealing of the cells. The electrolyte is deposited into the top of the cell casing by the filler tube of a dispenser. In order to ensure that a cell is completely filled with the electrolyte prior to closing and sealing the cell casing, the electrolyte must be allowed to percolate through the separator from the top of the cells.
However, because the electrode and separator layers are usually very tightly wound, the separator is compressed between the electrode surfaces, and the rate of penetration of the electrolyte through the separator is slow. Accordingly, the electrolyte filling step has introduced delays in the manufacturing operation since substantially more time may be required to permit the electrolyte to become absorbed by the separator than is taken by the other steps on the production line.
One attempt at increasing the process of absorption of the electrolyte liquid into the separator material has utilized a partial vacuum enclosing the cell, the electrolyte liquid being dispensed on the top of the electrode coil under the conditions of the partial vacuum. Thereafter, upon restoration of atmospheric pressure and the penetration of the electrolyte liquid into the separator material, it has been found that the cell was not adequately filled with the electrolyte, apparently because of the formation of voids within the separator material.